Creatine kinase is an enzyme found in all vertebrates. It catalyzes the reversible conversion of creatine + ATP to phosphocreatine + ADP. Phosphocreatine is generally acknowledged to be a reservoir of high-energy phosphate in tissues of high and fluctuating energy demand. There are four isoenzymes of creatine kinase: two cytosolic forms, brain (BCK) and muscle (MCK), and two mitochondrial (MiCK) forms, sarcomeric and ubiquitous. The MiCKs differ from the two cytosolic CK isoenzymes in that while the cytosolic CKs are solely dimeric in form, MiCK exists in a dynamic equilibrium between soluble dimeric and membrane-associated octameric forms. MiCK has been localized to contact sites connecting the inner and outer mitochondrial membranes in association with adenine nucleotide translocase (ANT) and porin. Due to its localization and enzymatic function, a role for MiCK in the transport of high energy phosphate out of the mitochondria has been proposed. The potential role MiCK plays in cellular bioenergetics makes the investigation and characterization of this protein critically important. The focus of my research is to characterize the protein-protein interactions involved in the unique oligomeric structure of MiCK. I also plan to investigate the role of protein-protein, and protein-membrane interactions in the functional significance of MiCKs membrane localization. Using MidasPlus and other modeling and homology analysis software provided through the Computer Graphics Laboratory at UCSF, I plan to investigate these structural and functional interactions. Until the final coordinates for the crystal structure of MiCK have been released, I plan to utilize these facilities to model structural interactions via homologies to other proteins similar to MiCK in structure and localization.